Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

204
FXUS63 KLOT 270445
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
1045 PM CST Thu Feb 26 2026

.KEY MESSAGES...

- Friday will be unseasonably warm and breezy with a threat for
  brush fire spread.

- A narrow band of snow may develop near the Illinois and
  Wisconsin state line on Saturday.

- A swath of accumulating snow may fall south of Interstate 80
  Sunday night.

- There is a growing signal for a period of spring-like warmth
  and periods of showers and thunderstorms during the first half
  of March.

&&

.DISCUSSION...
Issued at 109 PM CST Thu Feb 26 2026

This afternoon through Sunday:

A low-amplitude upper-level wave continues to move across the
region this morning, and has contributed to broken cloud cover
and even a few sprinkles. Temperatures have hence been slow to
warm today, though the expectation remains for most areas to
reach the lower 40s by mid afternoon. With our area on the
western side of a surface high pressure system centered over
southern Ontario, winds will remain out of the southwest with
speeds generally near or below 10 mph. Clouds should clear this
evening as the upper-level wave departs.

Tonight looks fairly quiet. The low-level pressure gradient
will gradually reoriented in response to pressure falls across
the Upper Great Lakes ahead of a vigorous upper-level clipper
system. Have noted a few CAMs hint at the threat for shallow
ground fog to develop toward sunrise, though suspect the
increasing low-level flow should provide just enough entrainment
of dry air into the nocturnal stable layer to prevent any
saturation. Overnight lows should fall toward the upper 20s to
lower 30s.

Tomorrow, the aforementioned clipper system will race across
central Ontario. Mostly sunny skies in tandem with aggressive
low-level warm air advection into the Great Lakes ahead of the
system (850mb temperatures rising some 6 to 8 degrees C in 24
hours) will boost highs into the low to mid 60s. Upward mixing
into the base of a strong low-level jet will also support
southwest winds gusting in the 30 to 35 mph range. If more
aggressive mixing scenarios play out (HRRR/RAP), gusts could
approach 45 mph. With antecedent dry conditions, the more
aggressive mixing scenarios would support a threat for brush
fire spread. Will forgo the issuance of a Fire Weather Watch
given conditions looks like they may flirt, but not definitely
meet, Red Flag Warning criteria anywhere for more than a few
hour period (conditions currently look less impressive compared
to last Wednesday). A cold front will race across the area after
sunset, driving temperatures downward toward the low to mid 30s
by daybreak Saturday.

Ensemble model guidance is in agreement that the leading
clipper system will establish deep cyclonic upper-level flow
along the US/Canadian border into the weekend. There remains a
signal for an expansive region of upper-level diffluence in the
right entrance region of an upper-level jet streak to develop
atop the low-level baroclinic zone draped across the Lower Great
Lakes on Saturday. As a result, would expect a deep layer of
frontogenesis to develop somewhere within the baroclinic zone,
supporting an elongated west-to-east band of snow. With a
residually dry low-level airmass across the region, snow may
struggle to reach the ground except where frontogenesis and
lapse rates are maximized. Taken together, the stage will be set
for a narrow (perhaps one to two-county wide) band of plowable
snow in the general region on Saturday. At this point, ensemble
guidance favors the band of snow materializing near the Illinois
and Wisconsin border. Also, cannot rule out additional bands of
snow, perhaps mixed with rain, developing elsewhere across the
region where secondary frontogenetical circulations interact
with a plume of steep mid-level lapse rates. So, will paint a
gradient in PoPs across the region ranging from likely (>55%)
near the Wisconsin border to slight chance (15%) near US-24.

Sunday looks comparatively quieter as a surface high pressure
system builds into the Great Lakes. Increasing high-level cloud
cover in advance of the next storm system materializing in the
central Plains will stunt highs to the lower 30s.

Borchardt


Sunday night onward:

The pattern next week and into the second week of March is
starting to look much more active as a parade of weather systems
traverse across the CONUS.

The first of these systems is expected to arrive Sunday night
into Monday in the form of a shortwave trough that is progged to
be moving across the mid-Mississippi Valley. While a surface
low is expected to develop with this wave, the low is currently
forecast to develop over the southern Plains closer to the
surface and mid-level baroclinic zones that are expected to be
draped over the Ohio and Tennessee River Valleys. What this
means for northern IL and northwest IN is that an arctic high
over the Ontario and the eastern Great Lakes will be pushing
drier low-level air into the region which may limit the coverage
of precipitation locally. That said, the combination of the
shortwave moving through and mid-level moisture still looks to
be sufficient to generate at least some precipitation,
especially over the southern half of the CWA. With temperatures
expected to be in the 20s precipitation is expected to fall as
snow and result in some accumulations. Given that there is some
uncertainty in snow coverage, it appears the better chances for
accumulations (40-50% chance of at least 1") will be south of
I-80 with lesser amounts expected north. Though, locally higher
amounts are possible especially closer to the aforementioned
baroclinic zone.

Snow is expected to taper Monday morning as the shortwave and
associated surface low progress eastward into the Mid-Atlantic.
However, the arctic surface high is expected to remain in place
which will keep temperatures on the seasonably cool side with
highs in the mid to upper 30s. Heading into Tuesday the more
active pattern will start to take hold as the next shortwave
trough digs into the western CONUS. While this shortwave is also
projected to eject into the mid-Mississippi Valley late Tuesday
into Wednesday, guidance varies on how far north the
aforementioned baroclinic zone forecast to be over the Ohio
River Valley will get. Therefore, there is a scenario in which
the bulk of any precipitation Tuesday night and Wednesday
remains well to our south in central and southern IL/IN but
there is also a chance for at least the far southern part of our
CWA to get brushed by some precipitation. For now the 20-40%
POPs offered from WPC centered mainly south of I-80 seems
reasonable at this range. Furthermore, depending on where this
baroclinic zone is may give us some mixed precipitation with
this shortwave mainly in the form of rain and snow.

From Wednesday onward the forecast will begin to trend warmer
and wetter as broader troughing establishes over the western
CONUS. This in turn will generate southwesterly flow across IL
and the Great Lakes allowing temperatures to warm above seasonal
values (typical highs for early March are in the lower 40s) and
closer to temperatures seen in April. In addition to the warmer
temperatures, this flow pattern will also favor any shortwaves
that break off the main trough to eject towards the Great Lakes
which would favor more weather systems in our area. That said,
guidance does continue to vary the exact track and timing of any
potential weather systems which does make this part of the
forecast more uncertain especially when it comes to
precipitation coverage and intensity. Regardless, given the
ensemble signal for this period of more stormy weather, we
recommend keeping a close eye on the forecast as we get closer.

Yack

&&

.AVIATION /06Z TAFS THROUGH 12Z SATURDAY/...
Issued at 1045 PM CST Thu Feb 26 2026

The only forecast concern remains strong/gusty southwest winds
Friday.

Light south/southwest winds overnight will steadily increase
after daybreak Friday morning with gusts into the mid 20kt range
by late morning. Gusts will increase into the 30kt range during
the afternoon and there may be a few hour period with gusts into
the mid 30kt range in the mid/late afternoon. These higher gusts
will depend on the potential for deeper mixing and confidence is
low at this time, but a short period of higher gusts may be
needed with later forecasts. Winds will turn westerly with
sunset and diminish with gusts 15-20kt expected Friday evening.
Winds will become northwest Friday evening and then more
northerly early Saturday morning, when gusts are expected to
end.

There is a chance for light/patchy fog overnight, mainly south
of the terminals but confidence remains low. Low level winds are
expected to remain strong enough to mix the low levels enough
to limit the fog potential but trends will need to be monitored.
cms

&&

.FIRE WEATHER...
Issued at 109 PM CST Thu Feb 26 2026

     Threat for brush fires on Friday...

On Friday, a vigorous storm system will race across central
Ontario causing strong southwesterly winds to develop across the
Lower Great Lakes. At this point, our forecast favors sustained
winds increasing toward 15 mph and gusts ranging from 30 to 35
mph. However, if more aggressive mixing scenarios pan out,
sustained winds could exceed 20 mph and gusts could exceed 45
mph. When paired with unseasonably warm temperatures in the low
to mid 60s and afternoon minimum relative humidity values of 25
to 30 percent, conditions may approach Red Flag Warning
criteria on a localized basis.

At this point, confidence in Red Flag Warning criteria being met
across a large area for a prolonged period of time is too low to
warrant the issuance of a Fire Weather Watch. However, burning
is still discouraged throughout the day on Friday to prevent the
uncontrolled spread of brush fires.

Borchardt

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Gale Watch from 10 AM CST Friday through Friday afternoon for
     Winthrop Harbor IL to Gary IN.

     Small Craft Advisory from noon Friday to midnight CST Friday
     night for Gary to Burns Harbor IN-Burns Harbor to
     Michigan City IN.

&&

$$

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